The present invention relates to a device for measuring an electric current using a solenoid with regular pitch in the form of a torus.
In the study of the media traversed by electric currents, such as electrolytes, plasmas, it is necessary to locate the lines of current and to know the intensities thereof. A conventional device which is used to measure a current distributed in space and passing through a surface, is constituted by a so-called "Rogowski" belt bearing on the contour of this surface. This belt is constituted by a toric solenoid coiled with a regular pitch and the voltage which is induced in this belt is integrated with respect to time, by an analog integrator or by a fluxmeter. The signal thus obtained or the indication of the fluxmeter is proportional to the current to be measured. A temporary variation of the current may thus be demonstrated, resulting for example its establishment or its interruption.
The coefficient of mutual induction between the coil constituting the long and narrow, closed toric solenoid, and a line of current traversing once, inside the solenoid, a surface bearing on the solenoid, is constant whilst it is zero if the line of current does not intersect said surface.
It is clear that a closed solenoid does not allow measurement of a permanent direct current flowing in an electric circuit since, topologically, the electric circuit on the one hand and the closed toric solenoid on the other hand cannot pass from a remote position to an interlaced position. However, the measurement can be made by using a deformable solenoid adapted to open without breaking the electrical continuity. In that case, operation is as follows: starting from the solenoid without current, it is opened, the current to be measured is surrounded and the solenoid is closed again. However, this procedure is possible only if the current to be measured is fixed in space or moves slowly. In the case of currents distributed in space and rapidly variable, this procedure is inapplicable.